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Date: Fri, 05 Oct 2012 14:06:17 +0530
From: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Organization: IBM
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To: Gleb Natapov <gleb@redhat.com>
CC: Avi Kivity <avi@redhat.com>, Jiannan Ouyang <ouyang@cs.pitt.edu>,
        Peter Zijlstra <peterz@infradead.org>, Rik van Riel <riel@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Marcelo Tosatti <mtosatti@redhat.com>,
        Srikar <srikar@linux.vnet.ibm.com>,
        "Nikunj A. Dadhania" <nikunj@linux.vnet.ibm.com>,
        KVM <kvm@vger.kernel.org>, chegu vinod <chegu_vinod@hp.com>,
        "Andrew M. Theurer" <habanero@linux.vnet.ibm.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Srivatsa Vaddagiri <srivatsa.vaddagiri@gmail.com>
Subject: Re: [PATCH RFC 1/2] kvm: Handle undercommitted guest case in PLE
 handler
References: <5061713D.5060406@redhat.com> <CAJocwcf+8u84_yDC-PK0Yni93YSTWzYvr69nq6b3pNv1MwVJzQ@mail.gmail.com> <50641356.5070008@redhat.com> <CAJocwcc19F+PtsQ5okGMvYeVnkEigpZRpwWY9JgeRPFqfcVoXA@mail.gmail.com> <506540C7.9070105@linux.vnet.ibm.com> <50680049.5020206@redhat.com> <20120930110755.GB1009@redhat.com> <50682945.3060309@redhat.com> <20121003141739.GA15253@linux.vnet.ibm.com> <506C5239.4080209@redhat.com> <20121004072900.GU23096@redhat.com>
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On 10/04/2012 12:59 PM, Gleb Natapov wrote:
> On Wed, Oct 03, 2012 at 04:56:57PM +0200, Avi Kivity wrote:
>> On 10/03/2012 04:17 PM, Raghavendra K T wrote:
>>> * Avi Kivity <avi@redhat.com> [2012-09-30 13:13:09]:
>>>
>>>> On 09/30/2012 01:07 PM, Gleb Natapov wrote:
>>>>> On Sun, Sep 30, 2012 at 10:18:17AM +0200, Avi Kivity wrote:
>>>>>> On 09/28/2012 08:16 AM, Raghavendra K T wrote:
>>>>>>>
>>>>>>>>
>>>>>>>>      +struct pv_sched_info {
>>>>>>>>      +       unsigned long   sched_bitmap;
>>>>>>>
>>>>>>> Thinking, whether we need something similar to cpumask here?
>>>>>>> Only thing is we are representing guest (v)cpumask.
>>>>>>>
>>>>>>
>>>>>> DECLARE_BITMAP(sched_bitmap, KVM_MAX_VCPUS)
>>>>>>
>>>>> vcpu_id can be greater than KVM_MAX_VCPUS.
>>>>
>>>> Use the index into the vcpu table as the bitmap index then.  In fact
>>>> it's better because then the lookup to get the vcpu pointer is trivial.
>>>
>>> Did you mean, while setting the bitmap,
>>>
>>> we should do
>>> for (i = 1..n)
>>> if (kvm->vcpus[i] == vcpu) set ith position in bitmap?
>>
>> You can store i in the vcpu itself:
>>
>>    set_bit(vcpu->index, &kvm->preempted);
>>
> This will make the fact that vcpus are stored in an array into API
> instead of implementation detail :( There were patches for vcpu
> destruction that changed the array to rculist. Well, it will be still
> possible to make the array rcu protected and copy it every time vcpu is
> deleted/added I guess.
>

If IUC, summary is, we are going with
- Let vcpu array be rcu protected.
- we use index inside vcpu and should be updated when a vcpu is
added/deleted.